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Title

Duffield_terminalinvestment_nuptialfoodgifts

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Description

Data for the tests of how injection with a non-pathogenic mortality cue mediates the gustatory appeal

AbstractInvestment in current versus future reproduction represents a prominent trade-off in life-history theory, and is likely dependent on an individual's life expectancy. The terminal investment hypothesis posits that a reduction in residual reproductive value (i.e., potential for future offspring) will result in increased investment in current reproduction. We tested the hypothesis that male decorated crickets (Gryllodes sigillatus), when cued to their impending mortality, should increase their reproductive effort by altering the composition of their nuptial food gifts (i.e., spermatophylaxes) to increase their gustatory appeal to females. Using a repeated-measures design, we analysed the amino acid composition of spermatophylaxes derived from males both before and after injection of either a saline control or a solution of heat-killed bacteria. The latter, although non-pathogenic, represents an immune challenge that may signal an impending survival threat. One principal component explaining amino acid variation in spermatophylaxes, characterized by a high loading to histidine, was significantly lower in immune challenged versus control males. The relevance of this difference for the gustatory appeal of gifts to females was assessed by mapping spermatophylax composition onto a fitness surface derived in an earlier study identifying the amino acid composition of spermatophylaxes preferred by females. We found that immune challenged males maintained the level of attractiveness of their gifts post-treatment, while control males produced significantly less attractive gifts post-injection. These results are consistent with the hypothesis that cues of a survival-threatening infection stimulate terminal investment in male decorated crickets with respect to the gustatory appeal of their nuptial food gifts.